Java Classes

In this section, you'll learn how to write your own Java classes, and how
to create objects from them. You've already made a start on classes in the
previous section. But we'll go into more detail now. In case you're confused
about the difference between an object and class, though, when we talk about
a class we're talking about the code itself, the code that sits around doing
nothing. When you put the code to work it's an object.

When you create a class, you're writing code to do a particular job. That
job might be to do with an employee, but not the company's sales figures at
the same time. You would write a separate class for the sales figures. That
way, you can re-use the employee class in another project. The sales figures
would be redundant data.

When you're trying to come up with your own ideas for classes you should
bear in mind that redundancy issue and ask yourself, "Is there any code
in this class that doesn't need to be here?"

For this section's example, we'll write a class that deals
with exams. For our example class, we'll make things simple. We'll record the
name of the person taking the exam, which exam it was, the score out of 50,
and a grade.

Let's make a start.

Create a new Java project for this. Call the package exams, and then
change the name of the Main method to ExamDetails. You should then
have the following code:

We'll create a second class to handle the exam data. So, in NetBeans, click
File from the menu bar at the top. From the File menu, select New
File. Highlight Java from the Categories list, and Java Class
from the File Types list. Then click Next. On the next screen, enter StudentResults
as the class name. Then click Finish. NetBeans will create a second class
in your project. You can delete any default comments.